Remove "vectorial" lib external dependency?

[lasagnaphil]

One of the good things about header-only libraries is that it can be trivially included in a project regardless of its build system (Visual Studio, cmake, make, ...). But having external dependencies can cause frustration for many people who just wanted an easy-to-include math library (Not everyone uses CMake.... Especially considering that a lot of the people in graphics / game development use Visual Studio)

It might be beneficial to move only the needed headers in the "vectorial" library inside the include folder to reduce this bloat. Or if having updateable submodules is still worth the bloat, then we can just do this only in the release distribution. (But as the external library isn't currently updated for about 3 years, I think it is safe to say that it wouldn't change over time.)

[stewartmiles]

@lasagnaphil vectorial is used if you're building with SIMD enabled. So if you wanted to ditch the dependency entirely you could do so by disabling that build option. Cmake exports to Visual Studio projects which you could include in your build - though Cmake still does add local paths in projects which is a pain.

w.r.t forking vectorial in this project, it's possible. @haroonq thoughts?

[haroonq]

Seems reasonable to me. Feel free to send a pull request that adds the vectorial library directly into the include/ folder.